With respect to a current mobile communications service (for example, a data service or a call service), an operator may provide multiple different services or packages for a user to select. After a user selects a service or a package, the operator uses a charging system (for example, an online charging system (OCS)) to perform charging for the service used by the user. In order to implement precise management of user accounts by means of unified charging, a user generally belongs to a charging system. However, the charging system is related to the service or package provided by the charging system. Services or packages that can be provided by charging systems vary with capabilities of the charging systems. Consequently, services or packages available to a user are limited by capabilities of charging systems that provide services for the user. If a user needs to use a service provided by a new charging system, the user has to be switched to the new charging system before the user can use the service provided by this charging system.
For charging system switching in the prior art, cutover can only be performed once, that is, all users on an old charging system are switched onto a new charging system all at once, and subsequent charging requests of the users are completely processed by the new charging system.
Defects of this switching manner may be identified as follows. Switching generally refers to switching a user from an old charging system to a new charging system that has a higher capability, and after switching, the new charging system processes all charging requests of the user, and the two charging systems cannot perform charging for the same user. After the capability of the charging system is upgraded, all users on the old charging system are switched to the new charging system, but not all users choose to use a new service or package. For a user who still uses an original service or package, the capability of the old charging system is absolutely adequate, and a significant waste of resources is caused if the old charging system is discarded. The two defects may be summarized into one, that is, the existing charging system switching cannot implement coexistence of two charging systems.